The Insul-Plug insulated chimney plug blocks old, unused thimble holes in masonry chimneys. It provides a thermal break from combustibles and prevents downdrafts from coming through the chimney.
The Insul-Plug is constructed of a ceramic based fireproof insulating material. The outer black plate covers up to a 10" diameter opening.
Simply insert it in the unused thimble opening and tighten the expansion screw on the front. The sides expand creating a tight fit in side the opening.
6" Insul-plug adjusts from 5 3/4" to 6 1/8"